The invention was developed in connection with the electropolishing of metal tubes, including tubes of stainless steel, for use in manufacture of pharmaceuticals, in which smooth, contaminant-free surfaces are desired.
However, it will be understood that the apparatus of the present invention is to be used to electropolish the interiors of tubes for a variety of purposes and uses outside of pharmaceutical processes.
In general, electropolishing is a process in which metal surface irregularities are removed by anodic dissolution in a suitable electrolyte. An electrolyte is an ionic conductor, i.e., a non-metallic electrical conductor in which current is carried by the movement of ions. With proper selection of agitation, current density, exposure times, specific gravity of the solution, temperature of the solution, and other conditions, the metal surface is smoothed and brightened while metal is removed.
During the electropolishing process, higher projections on the metal surface are removed faster than the lower projections, creating a leveling action. The removal of higher projections is called macropolishing, while the removal of the lower projections is called micropolishing. In electropolishing, both micro- and macro- asperities are preferentially removed. The removal or reduction of the surface micro-asperities increases the surface brightness and reflectivity and reduces surface friction, while the metal smoothness is determined by macropolishing.
In the past, electropolishing has been carried out by immersing the metal object to be electropolished in a tank of electrolyte and applying electropolishing current thereto. However, this has been found cumbersome or otherwise unsatisfactory when it is only the interior of a hollow metal object which requires electropolishing and when the object is more than a few feet long, in which case the required size of tank is excessive.
Bachert U.S. Pat. No. 4,025,447, Bartlett U.S. Pat. No. 2,475,586 and Farren U.S. Pat. No. 2,764,540 each disclose an apparatus for electropolishing a generally cylindrical surface of an object, in which the apparatus includes an electrode disposed approximately concentrically within the object, means for causing a continuous flow of electrolyte between the electrode and the surface to be polished, and an arrangement for applying an electric potential between the electrode and the object. The Bachert patent also discloses in FIG. 2 the provision of radially extending, insulated bristles 11 which help to maintain the concentricity of the electrode within the object. No provision is made for rotating the object.
Farren U.S. Pat. No. 2,764,540 and Zubak U.S. Pat. No. 3,533,926 each disclose a flow-through support for locating the center electrode rod radially in a cylinder, although not for relative rotation.
Roth U.S. Pat. No. 4,014,765 supports for rotation a hollow body to be electropolished, but the entire hollow body to be electropolished is immersed in a tank of electrolyte.
However, the prior devices have not been found entirely satisfactory for electropolishing of elongate metal tubes.
Accordingly, the objects and purposes of the present invention include provision of:
(1) Apparatus for electropolishing elongate metal tubes, including stainless steel tubes, and including commercially available tubes of high length to diameter ratio, for example tubes of up to 20 feet long and longer and having a diameter in a wide range of diameters.
(2) Apparatus as aforesaid capable of simultaneously and continually applying rotation, electric current and flowing electrolyte liquid to the tube to be electropolished while simultaneously and continuously removing therefrom gases produced in the electropolishing operation, for enhanced uniformity and reliability of electropolishing.
(3) Apparatus as aforesaid capable of simultaneously obtaining a similar electropolishing effect on more than one workpiece tube.
(4) Apparatus as aforesaid having a tube support of adequate length for handling elongate tubes but wherein the apparatus can be readily partially disassembled into and reassembled from shorter segments for storage during periods of non-use or movement from location to location.
(5) Apparatus as aforesaid which can be constructed using only relatively simple materials and tools.
Other objects and purposes of this invention will become apparent to persons acquainted with apparatus of this general type upon reading the following specification and inspecting the accompanying drawings.
The objects and purposes of this invention are met by providing an apparatus to internally electropolish tubes. Means horizontally support and rotatably drive at least one elongate tube for rotation about its length axis. Means at opposite ends of the tube respectively supply and allow outflow of electrolyte liquid. Means support an elongate cathode rod within the tube, the cathode rod being fixed and the tube rotating about it. An electric current supply has positive and negative connections to the tube and cathode rod which, in cooperation with the rotation of the tube and flow of electrolyte liquid therethrough, provide for electropolishing of the tube interior.